Many manufacturing operations generate extremely large quantities of water containing heavy metals or other contaminants. For instance, mining drawdown wells which are used to dewater deep mining operations are known to generate up to 75,000 gallons per minute (gpm) of water. Often this water contains heavy metals or other impurities which must be removed from the water before it can be safely discharged into the environment.
Current techniques for treating drawdown wastewater include large settling ponds, clarifiers, and sand filter systems utilizing iron or aluminum chemistry with large quantities of polymer additives. Such systems are able to demonstrate 90% compliance to discharge regulations. For example, arsenic cannot be safely discharged into the environment unless its concentration is less than 50 ppb ("parts per billion"). If influent arsenic levels are greater than 300 ppb, clarifier and sand filter systems are not able to consistently provide discharge levels less than 50 ppb. To achieve this level of arsenic reduction, chemical coagulants are required to form heavy and large particles, typically greater than 200 microns in size. However, such systems are subject to biological fouling, sand settling, and upsets. Upsets result in out of compliance water. In addition, system maintenance is extensive, with very large land areas required for the system installation.
Filters have been considered to remove metal contaminants from wastewater. For example, traditional microfiltration membranes have a pore size of about 0.5 microns with a flux rate of 100-200 GFD ("gallons per square foot of membrane per day"). At this flux rate, it would be necessary to have a membrane of at least 180,000 square feet to process 25,000 gpm of wastewater. If the wastewater flow rate is 75,000 gpm, then the membrane size would need to be at least 540,000 square feet. Such membrane sizes are prohibitively large and expensive.
It would be a significant advancement in the art to provide a process and system for removing metals and other contaminants from large quantities of wastewater.
It would be a major advancement in the art to provide a process and system for removing metals and other contaminants from large quantities of wastewater which do not require large land areas.
It would also be an important advancement in the art to provide a process and system for removing metals and other contaminants from large quantities of wastewater which consistently complies with environmental discharge requirements.
Such processes and systems are disclosed and claimed herein.